Asymmetric cell division is required for development and pattern formation in multicellular organisms. In many organisms, the first zygotic division is asymmetric, resulting in daughter cells with different embryonic fates. Although experimental manipulation of zygotes in many systems is difficult, the brown alga Fucus distichus provides an excellent model organism for dissecting the development of asymmetry from an apolar progenitor cell. Actin microfilaments are essential for asymmetric growth in Fucus. Recent experiments have led to a model for axis fixation and development in Fucus in which formation of an axis stabilizing complex (ASC) with structural and functional similarity to mammalian focal adhesions is required. The factors comprising the ASC have not yet been identified in Fucus or in higher plants. In order to identify Fucus ASC components that bind actin, a two-hybrid screen will be performed. In addition, a Fucus cDNA library will be used to complement S. cerevisiae mutants with cytoskeletal and morphological defects. Factors identified in the screens will then be tested for actin binding activity in vitro. Antibodies raised against the actin-binding proteins will be used for localization in situ, and will be microinjected into developing zygotes to observe the resulting effects on establishment of Fucus polarity. The identification of actin-binding proteins from Fucus and the characterization of the roles in asymmetric morphogenesis will provide a model for the role of the actin cytoskeleton in zygotic development in complex multicellular organisms.